A force-limited seat belt can limit the force which the fabric belt applies on a human body by certain force-limiting structures when a vehicle crash happens.
In the second embodiment of the European Patent whose document no. is EP1607288B1, a seat belt apparatus comprises a U-shaped frame, a reel and a torsion bar which is in the form of a rod or rods and is provided in the reel.
An important feature of the above patent lies in that when the reel is in a locked state, two ends of the reel are locked by the external teeth being engaged with the internal teeth in the U-shaped frame, the torsion bar is fixed inside the spindle and with two end covers, the torsional deflection distributes uniformly on the whole torsion bar, thus producing the force-limiting effect.
By referring to the above European patent literature, the specific details of force limiting installation apparatus in the above patent literature can be obtained.
However, with respect to the force-limiting installation apparatus disclosed in the above patent literature, the torsion bar extends outside of the end cover, the mechanical characteristics are complex, which is adverse to the sustainable property of the distortion of the torsion bar; incidentally, the property of two-level increasing force-limiting and two-level decreasing force-limiting cannot be achieved.